This invention relates generally to a recording and/or reproducing apparatus in which a rotating recording medium is used. More particularly, the invention relates to a recording head driven by a pulse motor which head intermittently steps over a rotating recording medium. The pulse motor is driven by unbalanced excitation.
Heretofore, an apparatus has been used for obtaining video pictures which are reproduced at any speed by previously rotating a disc-formed, magnetic recording medium at high speed and in synchronism with the vertical synchronizing signal of a video signal. A magnetic head intermittently steps over and in contact with the surface of the recording medium. The head steps radially to form concentric, circular recording tracks. One field signal or a plurality of field signals are recorded on each track. At the time of reproducing, the speed of the reproduced picture is changed by varying the moving speed of the magnetic head.
The intermittent movement of the magnetic head is ordinarily accomplished by a pulse motor which turns through a predetermined rotational angle, which is a displacement proportional to the number of input pulses. The stopping position of this pulse motor is determined by its construction, and by the number of input pulses. Accordingly, there is no necessity for a servo-loop giving a positional detection of the stopping position. Therefore, this pulse motor accomplishes a simple control with an open loop, in accordance with the number of input pulses.
However, by the use of this pulse motor, the intermittent stopping positions of the magnetic head cannot be varied. For this reason, if a magnetic medium on which a video signal has been previously recorded is to be reproduced by another apparatus, of if a magnetic recording medium which has been recorded has been preserved for a long time and is to be reproduced by the same recording/reproducing apparatus, an accurate and positive tracking operation of the magnetic head becomes extremely difficult. Then, a normal reproduced picture cannot be obtained.
Furthermore, in order to cause the head to intermittently step over the recording medium in a manner such that the forward travel tracks and the return travel tracks are concentric and, at the same time, are mutually alternating, it is necessary to step by two track pitches at the time of ordinary stepping and to step by only one track pitch when the stepping direction is reversed. Accordingly, it has been the prior art practice to impress two driving pulses on the pulse motor at the time of ordinary head stepping and to impress a single pulse at the time of reversing the stepping direction. The changing of the number of applied pulses in this manner, necessitates a complicated circuitry.